North Fork Feather River Project



In-stream Bypass Flows Cooling Towers

Conceptual Feasibility Assessment



1.0          INTRODUCTION


One objective of the relicensing requirements for Pacific Gas and Electric Company’s (PG&E) North Fork Feather River Project is to reduce the temperature of water in the North Fork Feather River at identified compliance locations.  One alternative method of accomplishing this objective is to cool the in-stream bypass flows using cooling towers.  PG&E has requested Black & Veatch to perform a brief conceptual level feasibility assessment of this concept.




The following design criteria were provided by PG&E:

·        Feather River flow of 250 cfs is to be cooled 1 degree C (1.8 degree F.)

·        Incoming river water temperature is 22 C (71.6 F.)

·        Cooling is required during July and August.


The following criteria were assumed by B&V using public data available for the region but not specific to the project sites:

·        Design Wet Bulb temperature 64 F during July and August.

·        Cooling tower selected for 5 degree approach to wet bulb supply 69 F water.


3.0         SYSTEM DESIGN


·        Stream design flow 250 CFS (112,200 GPM) at 22C ( 71.6 F)

·        Temperature reduction required 1 C (1.8 F) or leaving water temperature 21C ( 69.8 F).

·        Heat rejection is 100,980,000 BTUH.

·        Cooling tower would require bypass pump back stream or upstream pond for fish transport.

·        Preliminary conceptual design with 14- 50' x 50' counter flow cooling tower cells with 200 Hp fans  and 14 - 400 Hp low head pumps.

·        Low velocity depth inlet water filter with bypass overflow stream.

·        The pump intake and overflow bypass requires special design for fish and temperature control.

·        Maintain cost for cooling towers verse chillers is about the same.

·        Double inlet tower’s height is about 75 feet with single row of cells Single inlet tower’s height is about 100 feet or two cells back to back. Height range is approximately 75-100 feet.

·        Site location and elevation of adjacent stream has major impact on tower height plus normal summer wind direction and trees or vertical walls.

·        Environmental siting will impact final cost of tower.


PG&E has indicated that cooling could be required at three locations-below the Rock Creek, Cresta and Poe dams.  The system described below would be typical for each location.  Total system requirement for the three locations would be three times the individual system.






Power requirements 5,500 kW, estimated annual usage 7,000,000 kWh or $455,000 per year per installation.





An estimated Construction Cost Budget range for cooling towers, pumps, piping, stream dam with sand filter and bypass overflow stream is $9.8 to $13.5 million per stream. Tower will not maintain 69.8 F or less if stream flow is above 250 CPS or wet bulb is above 65 F. These estimated costs are for a typical installation.  They do not address the confined site conditions along the Feather River, architectural appearance, or other potential mitigation measures required to allow construction at these sites.   They also do not include costs for utilities including the transmission lines to bring power supply to each site. 



Each site will require about 180,000 square feet (200' wide x 900' length).